Because it's not about the tool or the quality of the past contributions, but the quality of the current contribution. It's not new either, it's "show me the code" - it doesn't matter who you are, what you say, what you claim to have achieved in the past, the only thing that matters right now is this particular merge request and code.

I don't think the problem is the (AI generated) code per se, but as the article mentions, it's the human interaction. A reviewer can spend hours on reviewing the code and leaving feedback to the author, but if the author just feeds it into an AI (or worse, it's automatically fed into it) and processes it within seconds, only to start with a blank slate for a next change, what's the point of putting in all that effort?

Humans can learn and adapt, AIs can... ingest more stuff into their context, I suppose, but it's been proven that things break down if they have too much stuff in said context, and said context is limited.